1. Technical Field
This invention relates to the preparation and use of a magnetic printing master for use in preparing multiple copies of an original photopolymer image.
2. Background Art
It is known in the art of image reproduction to imagewise expose a photopolymerizable surface, to dust the surface with fine particles of dyes or pigments (toner) to form a visible image, and to thermally transfer this to the surface of a separate element or receptor. Toning of a photopolymerizable surface with magnetic iron powder for this purpose is disclosed in Burg and Cohen, U.S. Pat. Nos. 3,060,023 "Image Reproduction Processes" (1962) and 3,060,024 "Photopolymerization Process for Reproducing Images" (1962), while Chu and Cohen, U.S. Pat. No. 3,649,268 "Process for Forming Images by Photohardening and Applying a Colorant" (1972) disclose similar toning of a photohardenable surface. Heiart, U.S. Pat. No. 3,202,508, also discloses that magnetic iron may serve as a useful pigment for a transfer process involving a photopolymer layer protected by a cover sheet. Other modes of magnetic toning are known, e.g., Schreckendgust, U.S. Pat. No. 3,718,466 "Magnetic Development" (1973), Jellers and Malkani, U.S. Pat. No. 4,101,320 "Magnetic Imaging Method" (1978), and Vola and Draai, U.S. Pat. No. 4,207,101 "Process for Magnetically Transferring a Powder Image" (1980). However, these do not describe or suggest preparation of a magnetic master useful for multiple imaging by thermal transfer. The principal object of the present invention is to provide such a master, whereby the excellent image quality characteristics of photopolymers may be used in a dry printing process to produce multiple copies of an original image.